1. Field of the Invention
The present invention relates to a brake hydraulic pressure control apparatus for use in an anti-lock control for preventing the locking of vehicle wheels during braking and for traction control for preventing slipping of the driving wheels at the time of starting or accelerating the vehicle.
2. Description of the Prior Art
Anti-lock control apparatus is used for preventing the locking of wheels during braking of the vehicle to assure the security of steering properties and running stability of the vehicle and for reduction of braking distance. The control modes of such apparatus (i.e., a pressurization mode, a pressure reducing mode, and a hold mode) for controlling brake hydraulic pressure are determined in a response to electric signals representative of the wheel speed and are obtained from the wheels and speed sensors. The brake hydraulic pressure is controlled by a micro-computer which controls the opening or closing of hold valves (i.e., pressurizing or holding valves) and decay valves (i.e., pressure reducing valves), which are electromagnetic valves, in accordance with the control modes, so as to pressurize, hold or reduce the brake hydraulic pressure.
In general, vehicle anti-lock control methods are classified into several groups, such as, a four-channel control method for separately controlling four wheels of a vehicle, a three-channel control method for separately controlling front left and right wheels, but collectively controlling rear wheels, or a two-channel control method for separately controlling front and rear wheel group. Hold valves and decay valves of the same number as the number of control channels are required.
The number of the control channels change in accordance with the type of vehicle based upon performance and economic considerations. In the prior art, when the number of the control channels are changed, the master cylinder must too be changed.